crash beim speichern und beenden (themen-Auswahl) behoben

ui/tab_b_ui.py

@@ -335,17 +335,22 @@ class TabB(QWidget):
     def _disconnect_theme_collection_signals(self) -> None:
         """Trennt Signale der alten Theme-Collection sauber."""
         collection = self._connected_theme_collection
-        if collection is None:
-            return
-        for signal_name in ("mapThemesChanged", "changed", "themeChanged"):
-            signal = getattr(collection, signal_name, None)
-            if signal is None:
-                continue
-            try:
-                signal.disconnect(self._refresh_thema_combo_live)
-            except Exception:
-                pass
+        if collection is not None:
+            for signal_name in ("mapThemesChanged", "changed", "themeChanged"):
+                try:
+                    signal = getattr(collection, signal_name, None)
+                except RuntimeError:
+                    break
+                except Exception:
+                    continue
+                if signal is None:
+                    continue
+                try:
+                    signal.disconnect(self._refresh_thema_combo_live)
+                except Exception:
+                    pass
         self._connected_theme_collection = None
+        self._theme_signal_connected = False
 
     def _connect_theme_collection_signals(self) -> None:
         """Verbindet Signale der Theme-Collection für Live-Aktualisierung der Themenliste."""